\subsubsection{Single-point constraints.} \label{sc_sp_constraints}
A single-point constraint (SPC) enforces a single degree of freedom (normally associated with a node) to a specified value. In structural analysis we use single-point constraints to:

\begin{itemize}
  \item Constrain or enforce translations and/or rotations of nodes that correspond to structure supports.
  \item Impose constraints for displacements that correspond to symmetric or antisymmetric boundary conditions.
  \item Removal of DOFs that correspond to frozen nodes in evolutive problems wher some parts of the mesh are deactivated.
\end{itemize}
